1. Field of the Invention
The invention resides in the field of coal fired MHD eletrical power generators and more particularly relates to processes for seed recovery and desulphurization of the generator gaseous effluent.
2. Description of the Prior Art
The theory and practice of MHD electircal power generating systems is well known in the prior art. In such systems, an electrically conducting fluid is passed between a pair of electrodes in the presence of a strong magnetic field to produce an electrical voltage across the electrodes. Plasmas or ionized gases are particularly suitable fluids for this process and may be generated by the combustion of fossil fuels such as coal. In such coal fired generators, the exhaust (flue) gases are ultimately expended into the atmosphere constituting an open cycle system as opposed to a closed cycle system in which the conducting fluid is recycled back through the generator.
The highest combustion temperatures attainable with coal (about 3,000.degree. C.) produce an insufficiently ionized combustion product to generate a satisfactory electrical power yield. Consequently, to increase conductivity the hot combustion gas is seeded with a material which undergoes thermal ionization such as an alkali metal, preferably potassium, which ionizes easily at the prevailing temperatures. In consequential descriptions, the metal of the seed material will be designated as potassium since it is the most common alkali metal used. Rubidium and cesium metal may also be employed advantageously since the higher the atomic weight of the alkali metal, the better the ionization.
In the combustion of coal, a substantial amount of SO.sub.2 is formed from the sulfur contained in the coal in which the seeded system reacts with the seed material to form potassium sulfate. This material may be recovered from the gaseous effluent of the generator by electrostatic precipitation which has the effect of removing both the seed (potassium) and objectionable sulphur pollution from the spent combustion gases which are subsequently exhausted as a flue gas into the atmosphere.
It is then necessary to separate the potassium from the sulphur to allow potassium reseeding of the system combustor. One separation method which has been proposed in MHD system configurations is the use of a reduction reactor in which a synthesis gas of carbon monoxide and hydrogen are reacted with the potassium sulfate to yield essentially the products of hydrogen sulfide and potassium carbonate. An absorber/stripper separates the two products after which sulfide with the aid of oxygen (air) is converted to solid sulphur, water, and some sulphur dioxide (SO.sub.2) in a claus reactor. This process requires the supply of auxiliary gases, i.e. hydrogen, carbon monoxide, and oxygen, and results in at least some gases (SO.sub.2) containing sulphur still being exhausted into the atmosphere.
The invention described below is highly economical in that it eliminates the need for auxiliary gases, produces little objectionable secondary gases, and yields a commercially useful byproduct, sulphuric acid.